60 GHz wireless communications belongs to millimeter wave communication, and has advantages such as a large channel capacity, high transmit power, great directivity, and good international commonality, thereby having a good prospect of wireless application. In an aspect of millimeter wave standard formulation, at present, there are mainly U.S Institute of Electrical and Electronics Engineers (IEEE Institute of Electrical and Electronics Engineers, IEEE for short) 802.15.3c, 802.11ad and 802.11aj, European Computer Manufacturers Association (European Computer Manufacturers Association, ECMA for short) 387, standards that are being formulated by China Wireless Personal Area Network (China Wireless Personal Area Network, CWPAN for short) PG4 (60 GHz Project Group), and the like. Refer to FIG. 1, which is a schematic diagram of channelization used in IEEE 802.11ad and CWPAN PG4. There is only one type of channel bandwidth, that is, a channel bandwidth of 2.16 GHz, in the channelization used in IEEE 802.11ad, which includes channels numbered 1 to 4. There is only 5 GHz, that is 59-64 GHz, in the 60 GHz license-exempt frequency band allocated to China, which is smaller than a bandwidth of 7-9 GHz of other countries and corresponds to two physical channels, numbered 2 and 3, in 802.11ad. The 60 GHz frequency band channelization accepted by CWPAN PG4 is to further channelize the international 2.16 GHz bandwidth into two 1.08 GHz sub-channels. In this way, the 5 GHz bandwidth includes six logical channels with variable bandwidth, including two channels of the 2.16 GHz bandwidth and four channels of the 1.08 GHz bandwidth. The two channels of the 2.16 GHz bandwidth separately correspond to channels 2 and 3 in IEEE 802.11ad, and the four channels of the 1.08 GHz bandwidth are channels 5 to 8 shown in FIG. 1. Although channel 5 or 6 is different from channel 2 and channel 7 or 8 is different from channel 3, they are strongly interfering co-frequency channels of each other. When the 60 GHz frequency band channelization scheme proposed by CWPAN PG4 is used, there will be multiple interference channels. For example, for channel 2, in addition to large bandwidth channel interference brought by an exactly same channel, that is, channel 2, there is also interference brought by two small bandwidth sub-channels 5 and 6 that overlap channel 2. Channel 2 is a co-frequency large bandwidth channel of channel 5 or 6, and channel 3 is a co-frequency large bandwidth channel of channel 7 or 8; therefore, channel 2 or 3 may be referred to as a large bandwidth channel for short, and channels 5, 6, 7, and 8 may be referred to as a small bandwidth channel for short. Although beamforming used in IEEE 802.11ad has an inner interference suppression function due to a relatively narrow beam, a problem of interference still commonly exists in an office environment with dense work stations and co-frequency channel interference from a neighboring work station is still severe. In IEEE 802.11ad, a method for clustering between personal basic service set control points (Personal Basic Service Set Control Point, PCP for short) or access points (Access Point, AP for short) is proposed to solve the problem of interference between basic service sets (Basic Service Set, BSS for short). The following uses a PCP as an example for description. PCPs that have a decentralized clustering capability and run on a same channel may constitute a decentralized cluster. A PCP in the cluster may receive a directional multi-gigabit beacon frame (Directional Multi-Gigabit Beacon, DMG Beacon for short) and/or announcement frame that is sent by another PCP, includes scheduling information, and is of a 60 GHz technology, so as to schedule communication in a non-overlapping time period and reduce interference. However, the foregoing method is limited to only clustering between co-channel PCPs with equal bandwidth; when a large number of PCPs with different bandwidth and on difference channels exist, co-existence fails due to severe interference.
In the prior art, during formulation of 60 GHz technical standards by CWPAN PG4, Institute for Infocomm Research (Institute for Infocomm Research, I2R for short) in Singapore puts forward a network coexistence scheme supporting dynamic bandwidth control, where a small bandwidth PCP periodically sends a beacon frame on a large bandwidth channel so that a device complying with IEEE 802.11ad can detect a network beacon frame of a BSS running on a small bandwidth channel of the China 60 GHz frequency band. It should be noted that the beacon frame herein and in the following all refers to the DMG Beacon. Specific steps for implementing network coexistence in the prior art are as follows:
1. A quasi-second PCP, that is, a device that is to be a second PCP, joins a BSS of a first PCP; after becoming a member of the first PCP, the quasi-second PCP sends a large bandwidth channel L2 sharing request to the first PCP.
2. If the first PCP agrees to share the L2, the first PCP notifies the quasi-second PCP of time and a frequency for sending a beacon frame on the L2.
3. The first PCP sends a beacon frame in a first notification period (Notification Period, NP for short) period on the channel L2, and meanwhile the quasi-second PCP sends a beacon frame in a second NP period on the channel L2. The quasi-second PCP completes synchronization with the first PCP by receiving a time stamp in the beacon frame of the first PCP.
4. After a whole NP period consisting of the first NP period and the second NP period ends, a guard interval (Guard Interval, GI for short) is added for channel switching, where the first PCP and the quasi-second PCP separately return, within the GI, to small bandwidth channels S5 and S6 for the BSS to keep running, and corresponding small bandwidth BIs are separately a first SBBI and a second SBBI.
5. A time interval between two whole NPs, that is, an interval of sending a beacon frame on a large bandwidth channel is a variable beacon interval (Variable Beacon Interval, VBI for short). A VBI may include multiple first SBBIs and second SBBIs. In a last first SBBI and a last second SBBI included in the VBI, the first PCP and the quasi-second PCP generate a common quiet period QP, and repeat step 3 and step 4 in the QP, where the QP includes the GI, NP1, and NP2.
After completing the foregoing scheme, the first PCP and the quasi-second PCP that respectively run on the small bandwidth channels S5 and S6 become synchronization pair PCPs. When small bandwidth channels S5 to S8 are used, coexistence with an IEEE 802.11ad device can be implemented by sending, on large bandwidth channel L2 or L3, a common beacon that can be identified by the IEEE 802.11ad device.
However, the coexistence scheme in the prior art can only solve a problem that synchronization pair small bandwidth PCPs (Small Bandwidth PCP, SB-PCP for short) are detected by a large bandwidth PCP (Large Band PCP, LB-PCP for short). However, when the synchronization pair SB-PCPs join a co-channel small bandwidth cluster, a VBI overlaps with a data transfer interval in an SBBI, which causes a conflict between the VBI and the SBBI; in addition, it is not easy for the synchronization pair SB-PCPs to detect a beacon frame of a large bandwidth cluster, that is, it is not easy to monitor cluster synchronization information and control information of the LB-PCP, and therefore clustering on the large bandwidth channel fails.